Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis

Pore water profiles of total-CO₂, pH, PO^3?₄, NO^?₃ plus NO^?₂, SO^2?₄, S^2?, Fe²⁺ and Mn²⁺ have been obtained in cores from pelagic sediments of the eastern equatorial Atlantic under waters of moderate to high productivity. These profiles reveal that oxidants are consumed in order of decreasing energy production per mole of organic carbon oxidized (O₂ > manganese oxides ~ nitrate > iron oxides > sulfate). Total CO₂ concentrations reflect organic regeneration and calcite dissolution. Phosphate profiles are consistent with organic regeneration and with the effects of release and uptake during inorganic reactions. Nitrate profiles reflect organic regeneration and nitrate reduction, while dissolved iron and manganese profiles suggest reduction of the solid oxide phases, upward fluxes of dissolved metals and subsequent entrapment in the sediment column. Sulfate values are constant and sulfide is absent, reflecting the absence of strongly anoxic conditions.     

Simulation of a Summer Urban Breeze Over Paris

Numerical simulations for an anticyclonic summer episode in the Paris area have been performed at the meso- scale for a 48-hour period, and compared to observations from a dense operational observational network. The meteorological stations have been classified, according to the extent of urbanization of their surroundings, into four classes (central Paris, urban, suburban, and rural). The atmospheric model, coupled with an urban surface scheme, correctly reproduces the temperature (within 1 K from the observations) and humidity. The intense urban heat island during the night is also well represented.Following the validation, the model is used to quantify atmospheric effects of Paris on the boundary layer, through a comparison with a purely rural simulation. At night, the model simulates a neutral or even slightly unstable boundary layer to a depth of 200 m over the city. In contrast, a very stable layer formed in the countryside. During the day, the boundary layer was more turbulent and 500 m deeper over Paris; vertical velocities of up to 1 m s^-1 were created over the city. This leads to an urban breeze with convergence at low levels (with winds around 5 to 7 m s^-1), and divergence at the boundary-layer top (with similar wind speeds). The horizontal extent of the breeze reaches for more than 50 km from the city centre, and could have an important impact on pollutant diffusion in the area for calm days.Finally, three other spring cases are presented briefly. These show that an urban breeze develops if the synoptic wind is weak enough or disorganized; an urban plume develops otherwise.     

A study of class II methanol maser condensations in the star-forming region W48

The methanol-line spectra in two maser condensations at velocities ～41 and ～45 km/s in the star-forming region W48 have been studied. The intensity of the 2₀-3_?1 E (12.2 GHz) line is anticorrelated with that of the 5₁-6₀ A ⁺ (6.7 GHz) line: the intensity of the 5₁-6₀ A ⁺ (6.7 GHz) line is greater at ～41 km/s than at ～45 km/s, while the opposite is true of the 2₀-3_?1 E (12 GHz) line. The remaining class II methanol lines in this source demonstrate the same behavior as the 2₀-3_?1 E (12 GHz) line. This contradicts current concepts about the maser line intensities in various methanol transitions: according to model calculations, the intensities of all class II lines should vary in phase. This effect is confirmed for a large homogeneous sample of 67 sources. Possible explanations of the observed effect are proposed; one suggests the possible role of “transpumping” of the methanol-level populations in the maser condensations. The relationships between the variations of the 2₀-3_?1 E (12 GHz) and 5₁-6₀ A ⁺ (6.7 GHz) line intensities, which are present for all 67 sources considered, may indicate that the condensations are at different distances from the pumping source. The presence of condensations at various distances from the pumping source in all 67 sources can be understood if they are ice planets revolving in different orbits around massive stars or protostars.     

Methanol radio emission at millimeter wavelengths: New masers at 1.3 and 2.8 millimeters

The results of a search for maser emission in the methanol lines 8_?1-7₀ E at 229.8 GHz, 3_?2-4_?1 E at 230.0 GHz, 0₀-1_?1 E at 108.9 GHz, and in the J ₁-J ₀ E series near 165 GHz in star-forming regions are reported. At least two masers and two candidates have been detected at 229.8 GHz. Thus, methanol masers have been detected in the 1-mm band for the first time. At 108.9 GHz, masers have been detected toward G345.01+1.79 and possibly toward M8E as well. Thermal emission was found toward 28 objects. The 229.8-GHz sources are class I masers, whereas the 108.9-GHz sources are class II masers. An analysis using a large velocity-gradient method shows that the 229.8-GHz masers can appear at densities of about 3×10⁴ cm^?3. The ratios of the flux densities in different class I lines toward DR 21(OH) and DR 21 West can be approximated in models with gas kinetic temperatures of about 50 K. Detection of the 108.9 GHz masers toward G345.01+1.79 and M8E may provide information about the geometry of these objects.     

Modelled variability of the sea surface circulation in the North-western Mediterranean Sea and in the Gulf of Lions

A chain of three nested models, based on the MARS 3D code, is used to simulate the North-western Mediterranean Sea circulation with a finest grid of 1.2 km resolution and 30 vertical sigma levels. This modelling system allows to resolve the coastal dynamics taking into account the influence of the general basin circulation. The aim of this study is to assess the ability of the nested MARS-3D models to reproduce most of the circulation features observed in the North-western Mediterranean Basin and in the Gulf of Lions. Comparisons of modelled sea surface temperature and salinity with MEDAR/MEDATLAS climatology and NOAA/AVHRR satellite measurements show that the model accurately reproduces the large and coastal scale variability. Over the Northern Basin, the seasonal changes of the cyclonic gyre extension are correctly simulated, even though in summer, the modelled temperature of the surface layer remains in basin-average 1°C cooler than the satellite measured temperature. As soon as the stratification erodes, modelled and observed temperatures become closer. Over the Gulf of Lions, realistic coastal responses are obtained under different wind conditions. Upwellings are correctly located and their intensity and spatial extension were here improved by the use of Aladin wind fields (10 km spatial resolution) and the introduction of a drag coefficient fitted according to the stability of the planetary boundary layer. The dispersion of fresh Rhone water discharge and the mesoscale circulation simulated by MARS-3D also agree with satellite measurements.     

Velocity–porosity relationships: Predictive velocity model for cemented sands composed of multiple mineral phases

Computer simulations are used to calculate the elastic properties of model cemented sandstones composed of two or more mineral phases. Two idealized models are considered – a grain‐overlap clay/quartz mix and a pore‐lining clay/quartz mix. Unlike experimental data, the numerical data exhibit little noise yet cover a wide range of quartz/cement ratios and porosities. The results of the computations are in good agreement with experimental data for clay‐bearing consolidated sandstones. The effective modulus of solid mineral mixtures is found to be relatively insensitive to microstructural detail. It is shown that the Hashin–Shtrikman average is a good estimate for the modulus of the solid mineral mixtures. The distribution of the cement phase is found to have little effect on the computed modulus–porosity relationships. Numerical data for dry and saturated states confirm that Gassmann's equations remain valid for porous materials composed of multiple solid constituents. As noted previously, the Krief relationship successfully describes the porosity dependence of the dry shear modulus, and a recent empirical relationship provides a good estimate for the dry‐rock Poisson's ratio. From the numerical computations, a new empirical model, which requires only a knowledge of system mineralogy, is proposed for the modulus–porosity relationship of isotropic dry or fluid‐saturated porous materials composed of multiple solid constituents. Comparisons with experimental data for clean and shaly sandstones and computations for more complex, three‐mineral (quartz/dolomite/clay) systems show good agreement with the proposed model over a very wide range of porosities.     

The protection of karst water resources: the example of the Larzac karst plateau (south of France)

Wide karst plateaus extend in the carbonate rocks of the Grands Causses area, north of Montpellier (south of France). They are surrounded by a hard rock base that feeds important rivers, such as the Tarn River and tributaries, and crosses the plateaus creating deep gorges. The Larzac plateau, the most southern, makes a link with the Mediterranean region. It is traversed by one of the main national roads and another main road under construction from Clermont-Ferrand to Montpellier and Spain. The karst water resource of the plateau, from springs, is used as a water supply for the Millau area (30,000 inhabitants); but it also recharges surface rivers, mainly during the summer and fall when the water level is low, in a region that is well known for water recreation activities, for fish farming and, above all, for sheep farming and Roquefort cheese production. The fundamental question was should the karst and its water resource be fully protected by strict regulations (for example as a nature reservation) in land-use management of the plateau based upon the knowledge of its hydrogeological functioning and its karst structure? Decisions, concerning the ～500-km² area were elaborated from detailed hydrogeological studies, which included natural and artificial tracing, analysis of karst aquifer functioning, landscape analysis, and risk assessment and mapping. Recommendations were proposed to local and regional decision makers to define what were the preferences in terms of water resource protection and water quality restoration. Following such an approach in a karst area is not easy for hydrogeologists or for decision makers. In non-karstic regions, protection zones currently extend over small areas of a few square kilometers, which can be easily placed under the control of a small municipality. In the present example, the main water supplies are two springs that recharge areas that extend respectively over 100 and 110?km². Included are several municipalities, some of which use them for their water supply, whereas others are concerned with pollution risks and land management projects. The recent French Water Act, which considers water as a common heritage, allows for general management by all the users, and it deals with the water and the terrain in which it flows. The regulation tools seem very well suited to karst region management. However, time is needed to educate users and decision makers, and with the help of karst scientists, to work together in a framework that is larger than the usual municipal limits.     

Urban Thermodynamic Island in a Coastal City Analysed from an Optimized Surface Network

Within the framework of ESCOMPTE, a French experiment performed in June and July 2001 in the south-east of France to study the photo-oxidant pollution at the regional scale, the urban boundary layer (UBL) program focused on the study of the urban atmosphere over the coastal city of Marseille. A methodology developed to optimize a network of 20 stations measuring air temperature and moisture over the city is presented. It is based on the analysis of a numerical simulation, performed with the non-hydrostatic, mesoscale Meso-NH model, run with four nested-grids down to a horizontal resolution of 250 m over the city and including a specific parametrization for the urban surface energy balance. A three-day period was modelled and evaluated against data collected during the preparatory phase for the project in summer 2000. The simulated thermodynamic surface fields were analysed using an empirical orthogonal function (EOF) decomposition in order to determine the optimal network configuration designed to capture the dominant characteristics of the fields. It is the first attempt of application of this kind of methodology to the field of urban meteorology. The network, of 20 temperature and moisture sensors, was implemented during the UBL-ESCOMPTE experiment and continuously recorded data from 12 June to 14 July 2001. The measurements were analysed in order to assess the urban thermodynamic island spatio-temporal structure, also using EOF decomposition. During nighttime, the influence of urbanization on temperature is clear the field is characterized by concentric thermo-pleths around the old core of the city, which is the warmest area of the domain. The moisture field is more influenced by proximity to the sea and airflow patterns. During the day, the sea breeze often moves from west or south-west and consequently the spatial pattern for both parameters is characterized by a gradient perpendicular to the shoreline. Finally, in order to assess the methodology adopted, the spatial structures extracted from the simulation of the 2000 preparatory campaign and observations gathered in 2001 have been compared. They are highly correlated, which is a relevant validation of the methodology proposed. The relations between these spatial structures and geographical characteristics of the site have also been studied. High correlations between temperature spatial structure during nighttime and urban cover fraction or street aspect ratio are observed and simulated. For temperature during daytime or moisture during both daytime and nighttime these geographical factors are not correlated with thermodynamic fields spatial structures.     

Alternative technologies for rural areas–what about the ‘alternative’ dimension of Wi-Fi?

Summary  The question of alternative technologies for high-speed Internet access lies at the heart of rural development problems. In this paper, we focus on one of those technologies, the system combining satellite technologies and Wi-Fi. Based on an empirical study carried out in three rural areas, we analyze the dynamics of the use and appropriation of that technology by the companies and organizations participating in the experiment. Considered both from a technical and social standpoint, the technology ‘in use’ appears here in its structuring dimensions.